Correct Answer: B

Rationale: Cerebrospinal fluid is the protective fluid that surrounds the brain and spinal cord. It acts as a cushion to protect these vital organs from injury and provides nutrients to the nervous system. Blood, plasma, and myelin are not the fluids specifically surrounding the brain and spinal cord. Blood is found within blood vessels, plasma is the liquid component of blood, and myelin is a fatty substance that forms a protective sheath around nerve fibers.

Correct Answer: B

Rationale: A) Incorrect. DNA is double-stranded, but RNA is typically single-stranded. B) Correct. DNA contains deoxyribose sugar, which lacks an oxygen atom on the 2' carbon of the sugar ring, while RNA contains ribose sugar, which has an additional hydroxyl group on the 2' carbon. C) Incorrect. RNA contains the nitrogenous base uracil, while DNA contains thymine. D) Incorrect. DNA and RNA have distinct structures and functions, so they are not identical molecules.

Correct Answer: B

Rationale: The Hardy-Weinberg equilibrium describes a theoretical population in which allele frequencies remain constant from generation to generation, indicating that the population is not evolving. This equilibrium occurs under specific conditions: no mutation, no gene flow, random mating, a large population size, and no natural selection. In this scenario, all genotypes are in proportion to the allele frequencies, and genetic diversity is maintained. Options A, C, and D do not accurately describe a population in Hardy-Weinberg equilibrium. Option A suggests rapid evolution due to strong directional selection, which would disrupt the equilibrium. Option C mentions a founder effect, which can reduce genetic diversity but is not a characteristic of a population in Hardy-Weinberg equilibrium. Option D describes a population dominated by a single homozygous genotype, which also does not align with the genetic diversity seen in a population at Hardy-Weinberg equilibrium.

Correct Answer: D

Rationale: The correct answer is D: Seminal vesicles. Seminal vesicles are responsible for producing a significant portion of the fluid that makes up semen, providing nutrients and protection for the sperm. While the testes produce sperm, the scrotum is the external sac that holds the testes, and the prostate gland also contributes to semen production but is not solely responsible for it.

Correct Answer: A

Rationale: Peroxisomes are membrane-bound organelles found in eukaryotic cells that contain enzymes involved in various metabolic processes. One of the main functions of peroxisomes is to break down hydrogen peroxide, a toxic byproduct of metabolism, into water and oxygen through the action of the enzyme catalase. This process helps protect the cell from oxidative damage caused by hydrogen peroxide. While peroxisomes are involved in other metabolic functions such as lipid metabolism and the synthesis of bile acids, their primary role is the breakdown of hydrogen peroxide. Choices B, C, and D are incorrect because peroxisomes are not primarily responsible for synthesizing lipids, packaging and transporting proteins, or storing genetic material within the cell.